1. Field of the Invention
The present invention relates to high voltage extenders for connecting a high voltage source to a spark plug. More particularly, the present invention relates to extenders that are used for insulating a conductive rod that is connected to an ignition coil at one end and to a spark plug at an opposite end.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.
Extenders are often used for the connection of high voltage sources, such as ignition coils, to spark plugs. These high voltage extenders are intended to pass the charge from the high voltage source (having a maximum voltage of 40 KV) to the ignition coils. Typically, these extenders are suitably insulated so as to prevent tracking from the conductive rod to the electrical ground created by the engine block.
FIG. 1 illustrates one example of a prior art high voltage extender utilized and sold by Caterpillar, Inc. The high voltage extender 10 has a machined stainless steel rod 12 that has a threaded end 14 and a connecting end 16. The threaded end 14 is machined onto the stainless steel rod 12 so as to connect into the female thread of the high voltage connector of an ignition coil. The connection end 16 connects to the high voltage terminal of a spark plug. A spring 18 is affixed to the connection end 16 of the stainless steel rod 12. The connection is accomplished by compressing the voluted spring 18 against the high voltage terminal of the spark plug. The spring 18 is received within a stainless steel cup 20 which is attached to the stainless steel rod 12. The rod 12 is pressed into a machined sleeve 22 of “void free” polytetrafluoroethylene, otherwise known as TEFLON™. The sleeve 22 serves to insulate the stainless steel rod 12 from the electrical ground created by the ignition block.
As can be seen in FIG. 1, the sleeve 22 has a narrow diameter portion 24 overlying the threaded end 14 of the stainless steel rod 12. A main section 26 of the sleeve 22 extends along the rod 12 from the narrow diameter portion 24. The main section 26 has a greater diameter than the diameter of the narrow diameter portion 24. The sleeve 22 defines a receptacle 28 at an end opposite the narrow diameter portion 24. Receptacle 28 is suitable for receiving a portion of a spark plug therein. An O-ring seal 30 is received within a notch 32 formed in the interior wall of receptacle 28 at the end of the sleeve 22. The sleeve 22 has a constant diameter extending from the narrow diameter portion 24.
Experiments with the prior art of FIG. 1 have determined that during extended periods of high-voltage (30-40 kV), the voltage punctures the polytetrafluoroethylene sleeve at a point where the stainless steel cup 20 is nearest the high voltage terminal of the spark plug. This occurs in an average of 5 to 10 hours when a grounded metal sleeve is placed over the extender 10. During thermal cycling, the polytetrafluoroethylene expands and contracts lengthwise and creates a gap at the inner face surface of the extender 10 and the insulating surface of the high voltage connection of the ignition coil. This allow tracking along the surface to the electrical ground created by the engine block. During shipping, the extender 10 has a tendency to loosen. This also serves to create a gap at the area of the interface of the ignition coil and the extender 10. The polytetrafluoroethylene material “cold flows.” This allows the extender 10 to loosen.
In the past, various U.S. patents have issued relating to such high voltage extenders. For example, U.S. Pat. No. 4,944,259, issued on Jul. 31, 1990 to R. D. Richardson, teaches an ignition system with an insulated and extendable extender. This extender resiliently biases the extender between the source of high energy and the spark plug to provide a positive and reliable electrical connection therebetween. The extender is of a relatively rigid construction so as to prevent bending. The extender is combined with a shield in the engine to further protect and increase the functional life of the components.
U.S. Pat. No. 5,060,624, issued on Oct. 29, 1991 to Bruning et al., provides an engine ignition system that has a transformer assembly and positioning means. The transformer assembly has an elongated body having a cup portion containing the coils, a base portion, and a stem portion. A conducting core extends through the stem and base portions. A suitable clip connects the core electrically to a spark plug installed in a profiled bore of the cylinder head. A positioning device is provided to positively align and contain the transformer assembly within a valve mechanism compartment defined between the cover and the cylinder head. A spring member connected to the cup portion. Depending guide members formed within the cover cooperate with each other.
U.S. Pat. No. 5,357,233, issued on Oct. 18, 1994 to Z. Wada, teaches an extension device which extends from the ignition coil to supply the peak high-voltage output to a spark plug. A part of an outer periphery of the secondary coil at an intermediate position of the outer periphery of the secondary coil sinks in relation to the other part of the outer periphery of the secondary coil to form a groove extending in a radial direction of the secondary coil. The peak high-voltage output is transmitted from the secondary coil through the groove to the extension device. The extension device includes a first member extending from the ignition coil, a second member for being connected to the spark plug, and an elastic member connecting the first member to the second member so that the first member moves elastically in relation to the second member.
U.S. Pat. No. 5,577,921, issued on Nov. 26, 1996 to Philyaw et al., discloses an electrical connector system for electrically connecting a voltage source to a spark plug terminal. This transformer assembly has an elongate body including a cup portion containing primary and secondary coils, a base portion, and a stem that is adapted to be installed in a housing of a cylinder head. An electrical source extends through the stem and base portion. An electrical connecting system includes an electrical conductor adapted to receive the voltage source with a spring contacting the end of a spark plug terminal biasing the conductor in a direction away from the spark plug. The electrical connector system further includes a positioning device adapted to positively align and contain the transformer assembly within a valve mechanism compartment defined between a cover and the cylinder head. A spring member is connected to the cup portion so as to axially bias the electrical conductor in a direction toward the spring in contact with the spark plug terminal so as to ensure an electrical connection.
U.S. Pat. No. 5,685,282 issued on Nov. 11, 1997 to Murata et al., discloses an ignition device for an internal combustion engine. This ignition device has a spark plug including a high voltage terminal, an ignition coil for generating a high voltage, and adapter assembly for electrically connecting the ignition coil to the high voltage terminal of the spark plug. The adapter assembly has a support sleeve for accommodating and supporting the high voltage terminal of the spark plug against a transverse movement of the high voltage terminal. The support sleeve is either a continuous extension or a metal tube of the adapter assembly. The assembly may also include a wear-resistant material.
U.S. Pat. No. 6,068,495, issued on May 30, 2000 to F. Virchow, discloses a sparkg plug for an internal combustion engine. A connector sleeve is formed of an insulating material. An elastic member is connected to the connector sleeve so as to seal the gap between the connector sleeve and a spark plug well. A ceramic inlet is formed in the connector sleeve so as to enclose the plug-in contact and the ignition cable connection.
U.S. Pat. No. 6,340,303, issued on Jan. 22, 2002 to Hamada et al., describes a high tension connection for the spark plug of an internal combustion engine. This connection portion has a first high tension connection terminal, a second high tension connection terminal for electrically connecting with the first high tension connection terminal, a locking mechanism provided between the first high tension connection terminal and the second high tension connection terminal for restricting the separation therebetween in the axial direction, and a spring member disposed between the first high tension connection terminal and the second high tension connection terminal. This device serves to prevent an instantaneous breakdown of the connection if an external force is applied to the high tension portion.
U.S. Pat. No. 6,817,872, issued on Nov. 16, 2004 to S. M. Berg, describes a heat-protective spark plug extension. The extender includes an elongated body formed of heat resistant and electrically insulative material that extends between a spark plug engagement end and a spark plug wire connector end. A conductor is located within the body and includes a fitting adapted to releasably electrically connect to a spark plug wire. A receptacle is adapted for electrical connection to a spark plug. An adjustment part permits adjustable movement of the spark plug wire connector end relative to the conductive receptacle.
It is an object of the present invention to provide an extender which assures that the insulating material is void-free.
It is another object of the present invention to provide an extender which seals an interface between the extender and the ignition coil and serves to prevent high voltage leakage.
It is another object of the present invention to provide an extender which prevents movement of the rod within the sleeve rotationally and lengthwise.
It is still a further object of the present invention to provide an extender which is resistant to the corona created in the engine block.
It is a further object of the present invention to provide an extender which is easy to manufacture, easy to install and use, and relatively inexpensive.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.